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I've been reading up about NASA's Juno mission, and came across the Wikipedia article about JunoCam, which is Juno's onboard visible-light camera.

In the article, it's mentioned that the resolution of the sensor is 1200x1600 pixels, which comes out to just under 2MP.

Obviously, sending any camera into deep space and establishing a stable orbit around Jupiter is no small feat -- but seeing as Juno launched in 2011, why is JunoCam's sensor's resolution so low?

I'm assuming - maybe too optimistically - that design changes like sensor selection would be finalized 4-5 years before launch. In 2006-2007, entry-level consumer DLSRs often sported 10MP sensors.

Basically;

  • Is it more difficult to harden a higher-resolution sensor against hazards in space?

  • If not, what reasons could NASA have to avoid using higher-resolution sensors?

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up vote 23 down vote accepted

There is one overriding requirement for deep-space missions: reliability. In general NASA Preferred Parts are quite stodgy, because the overriding need is for a mature, well-understood technology. Cutting-edge technology that doesn't work is frowned upon under the circumstances. So 10-year-old image sensors are about what you expect.

Additionally, if you read the JunoCam article you linked, you'll see (second paragraph, first sentence) that data transfer rates are quite slow, on the order of 40 MB per 11 days. Increasing image size cuts down the number of images which can be acquired, and I expect that a lot of effort went into determining the tradeoff between number of images and image resolution.

For what it's worth, NASA has been pushing for better data rates for its programs, but the limited power and long ranges involved make this a non-trivial problem. The LADEE mission a couple of years ago incorporated the LLCD (Lunar Laser Communication Demonstrator) which worked quite well, and this holds great promise (optical communication limit of 1 bit/photon at the receiver), so future missions may be able to do a lot better.

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2  
I don't think that upgrading the sensor itself 5 years before launch was impossible, but upgrading the sensor alone in the existing optical system won't help much. – Dmitry Grigoryev 22 hours ago
up vote 8 down vote

You seem to be under the impression that the quality of photos taken in space is limited by the sensor resolution, which is not the case. Equally important factors are the sensor sensitivity, which gets worse as you increase the pixel count, and the robustness of the optical system.

Simply put, if you were to send a 10MP DLSRs camera on Jupiter, it wouldn't be able to focus properly (or at all) after the vibrations it experienced during launch to the point where the actual sensor resolution wouldn't matter. Plus, it wouldn't get enough light to make quality photos.

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How would sensor resolution affect ability to focus? – loneboat 19 hours ago
3  
I didn't say it would. It's the other way around: the ability to focus defines the sensor resolution that is useful, and installing a higher-resolution sensor won't improve image quality. – Dmitry Grigoryev 18 hours ago
    
Aah, that makes sense. Thanks for the clarification! – loneboat 16 hours ago
up vote 4 down vote

Think more like 10 years before launch. Once it's designed, it's designed - changing components is a major risk factor and they're unlikely to want to do that. A massive amount of that time will have been spent on testing.

This is the appeal of small, semi-disposable satellites with cheap launchers going into Earth orbit - if you lose one then it isn't such a big deal. With massive investment in money and time getting this thing to Jupiter though, adding risk is generally Not A Good Thing.

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up vote 0 down vote

Also, diffraction at the optical aperture limits the usable physical pixel size to a relatively large value. The details are worth a few minutes of web research, as they also limit the effective resolution possible with the fine pixel pitch common in digital cameras, including DSLRs.

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up vote 0 down vote

The data transmission rate needs to be considered. It costs time and battery energy to send back whatever images you do collect.

To your first question: Yes: Protecting micro-electronics from hard radiation will be much more difficult as you reduce the size of a pixel and increase its susceptibility to ionizing radiation.

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